A player catches the ball between his knees and then does a somersault into the goal. The goalkeeper has no clear way to defend the goal. Is this legal?

USSF answer (August 24, 2011):
Players are not allowed to perform dangerous acts that deny other players a chance at the ball. (But similar acts that do not endanger other players (or officials) would seem to be legitimate.) If the act in question is reckless and places other players in danger, then the referee should stop play, caution for unsporting behavior, and restart with an indirect free kick for the goalkeeper’s team.